Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add lihtness/gnomon-mcp --skill gnomongit clone --depth 1 https://github.com/lihtness/gnomon-mcpWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/lihtness/gnomon-mcp/gnomon)<a href="https://agentmods.dev/skills/lihtness/gnomon-mcp/gnomon"><img src="https://agentmods.dev/badge/skills/lihtness/gnomon-mcp/gnomon/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/lihtness/gnomon-mcp/gnomon"><img src="https://agentmods.dev/badge/skills/lihtness/gnomon-mcp/gnomon.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00058 | $0.01082 |
| Opus 5 | $0.00029 | $0.00541 |
| Sonnet 5 | $0.00012 | $0.00216 |
| Haiku 4.5 | $0.00006 | $0.00108 |
Grade A, and why
gnomon scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 8d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 80 lines — stays where its author put it; the contents beside it link to each section on GitHub.
gnomon
gnomon-mcp exposes four MCP tools so the model computes deterministically instead of guessing.
Reach for gnomon whenever the answer involves
- The current date or time. Your training cutoff is not today. Call
now. - Elapsed time / time-until / time-since. Call
calendarwithdiff,until, orsince. - Date arithmetic (adding days/weeks/months/years, weekday lookups, business days, formatting). Call
calendar. - Natural-language dates ("next thursday", "in 3 hours", "last friday"). Call
calendarwithparse. - Arithmetic that matters — anything past trivial mental math: decimals, percentages, sums over many items, averages, statistics. Call
calc. - Unit conversion — metric/imperial, temperature, bytes, time durations. Call
calc_convert. Never eyeball.
The four tools
now(tz?) — current moment, rich dict
One call returns ISO, date, time, weekday, day_of_year, week_of_year (ISO), quarter, fiscal year (US gov), is_weekend, and more. Optional IANA timezone (defaults to UTC).
now() → UTC snapshot
now("America/Los_Angeles") → in a specific tz
calendar(ops) — batch date operations
Pass a list of {"op": NAME, ...args} dicts, get a list back in order. Use this for table-row workloads — one tool call covers a whole column.
calendar([
{"op": "until", "target": "2026-12-31", "unit": "days"},
{"op": "since", "source": "2026-01-01", "unit": "days"},
{"op": "diff", "start": "2026-01-01", "end": "2026-12-31", "unit": "days"},
{"op": "add", "date": "2026-05-25", "n": 1, "unit": "months"},
{"op": "weekday", "date": "2026-05-25"},
{"op": "business_days", "start": "2026-05-01", "end": "2026-06-01"},
{"op": "parse", "natural": "next thursday", "tz": "America/Los_Angeles"},
{"op": "format", "date": "2026-05-25", "fmt": "%A, %B %d %Y"},
])
Units for diff/until/since: seconds, minutes, hours, days, weeks.
Units for add: above plus months, years (calendar-aware via relativedelta).
business_days counts Mon-Fri (start inclusive, end exclusive); doesn't yet know holidays.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 8d ago First seen · 80 lines · 58 tokens per session scan A 877a8a99e729
gnomon is a skill published in the GitHub repository lihtness/gnomon-mcp (1 stars, last pushed 3mo ago), licensed MIT. It adds 58 tokens to every session and 1,082 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
Other skills, from other repositories
send-email
Compose and send a one-off email to a named recipient via Resend - written in the operator's voice, then sent in-run through the shared send caps with an operator audit copy.
skill-factory
A workflow that examines completed session work and turns reusable patterns into Claude Code skills.
session-wrap
Use when wrapping up a session before ending. 4 parallel subagents detect doc updates, repeated patterns, learning points, and follow-ups, then a verifier deduplicates and presents choices. Triggers on /session-wrap, session wrap, session cleanup, end of session.
caveman-help
Quick-reference card for all caveman modes, skills, and commands. One-shot display, not a persistent mode. Trigger: /caveman-help, "caveman help", "what caveman commands", "how do I use caveman".
relay
Session relay — compresses what's been done so far (writes a one-liner for /compact) and generates a "next task" prompt (a baton) for the user to hand off. Use on requests like "relay / hand off / next session / continue after compact / baton / handoff / clean up context and continue next task." Does not run /compact…
toolbox
Pre/post dev toolbox — named bundles of skills/agents loaded before development work and councils of experts invoked after. Run /toolbox or the toolbox.py CLI to list, activate, initialize, export, import, and validate toolboxes. Invoke at the start or end of a dev session, when setting up a new repo, or when sharing…